1. Field of the Invention
The present invention relates to a thermosetting resin composition and more particularly to a thermosetting resin composition excellent in processability and heat resistance.
Further, the invention relates to a thermosetting resin which is a component of said thermosetting resin composition.
Furthermore, the invention relates to a resin composition using as encapsulant for electronic component which are applications of above mentioned thermosetting resin composition.
2. Description of the Prior Art
Thermosetting resins are in use as casting, impregnating, laminating, and molding materials for various electric insulations and structures. In recent years, there has been the tendency of material service conditions to more severity in these applications and the heat resistance of materials has become an important property.
Conventionally, thermosetting polyimide resins are used for these purposes but their processing requires long-time heating thereof at high temperatures.
Epoxy resins improved in heat resistance, although superior in processability, are insufficient in high-degree heat resistance including mechanical and electrical properties at high temperatures and long-term resistance to thermal degradation.
An example of possible substitutes for these materials is a type of thermosetting resin comprising both a monomer having a double bond and a maleimide compound, as disclosed in Japanese Patent Publication Nos. 27806/83 and 15126/84. However, this type of resin needs to be converted into a prepolymer before thermosetting, because the above-mentioned monomer has a low molecular weight. When the resin is thermoset directly without the prepolymer conversion, there arises the problem of partial monomer vaporization taking place during the hardening. When the double bond-containing monomer has only one double bond in the molecule, the density of crosslinkage in the cured resin is limited and the cured resin is insufficient in heat resistance.
Other materials proposed include for example, a thermosetting resin mixture comprising a polyimide and an alkenylphenol and/or an alkenyl phenol ether (Japanese Patent Application Laid-Open No. 994/77) and a heat-resistant resin composition comprising a maleimide compound, a poly(allylphenol) compound and an epoxy resin (Japanese Patent Application Laid-Open No. 134099/78). These materials, however, have the problems of the cured products thereof exhibiting high permittivity and inferior water resistance, because the poly(allyl phenol) compound used in these materials is the Claisen rearrangement product of a poly(allyl ether) compound or has a structure which produces phenolic hydroxyl group through Claisen rearrangement during thermal curing. In addition, the ring-substituting alkyl group and either the ring-substituting hydroxyl group or ether residue are situated in positions ortho to each other on an aromatic ring and are liable to remain unreacted after curing particularly when the poly(allyl phenol) compound is of a novolak type, thereby affecting adversely properties of the cured products of the materials at high temperatures.